Enabling load balancing for MPLS-TP

ABSTRACT

A method of and a device for enabling load balancing for Multiprotocol Label Switching Transport Profile (MPLS-TP) are provided. The method is applied to a process of transmitting data between two Provider Edge (PE) devices that adopt a protection mechanism of primary and backup tunnels. The method comprises allocating, by a source PE device located at a head node of a tunnel, traffic to each of the primary and backup tunnels in a current transmission period based on transmission performance information about each of the primary and backup tunnels in a previous transmission period fed back by a destination PE device located at a tail node of the tunnel, when a set transmission period comes; and obtaining, by said source PE device, the traffic allocated to each of the tunnels and transmitting data to the destination PE device via the corresponding tunnels.

CLAIM FOR PRIORITY

The present application claims priority under 35 U.S.C 119 (a)-(d) toChinese Patent application number 201110232561.0, filed on Aug. 15,2011, which is incorporated by reference herein its entirety.

BACKGROUND

ITU-T (International Telecommunication Union TelecommunicationStandardization Sector) and IETF (Internet Engineering Task Force)specify an implementation of ITU-T transmission demand extendible IETFMPLS architecture. These extensions are referred to as MPLS TransportProfile (i.e. MPLS-TP where MPLS is the abbreviation for MultiprotocolLabel Switching).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a flow of balancing load according toan example of the present disclosure.

FIG. 2 is a schematic diagram of a format for an MPLS OAM message in anexample of the present disclosure.

FIG. 3 is a schematic diagram of tunnel aggregation in an example of thepresent disclosure.

FIG. 4 is a schematic block diagram of a PE device according to anexample of the present disclosure.

FIG. 5 is a schematic block diagram of a PE device according to afurther example of the present disclosure.

DETAILED DESCRIPTION

The MPLS-TP is a connection-oriented packet-switched network technology,which has the following features:

(1) switching paths using MPLS labels, and hence omitting complicatedfunctions of MPLS signaling and IP;

(2) supporting a multi-service bearer, being independent of a clientlayer and a control plane, and being capable of operating in variousphysical layer techniques; and

(3) having a strong transmission capability, such as QoS (Quality ofService), OAM (Operation, Administration and Maintenance), andreliability, etc.In a word, MPLS-TP=MPLS−L3 complexity+OAM+protection.

In order to support a connection-oriented end-to-end OAM model, manyconnectionless characteristics are excluded from the MPLS-TP, andprotection switching of ITU-T transmission style and an OAM function areadded, which are favorable for provision of services of atelecommunication level. Meanwhile, the MPLS-TP chooses some features ofan MPLS system that are favorable to data service transmission, abandonsa complicated control protocol family defined for MPLS by IETF,simplifies a data plane and omits an unnecessary forwarding processing,so that it is more suitable for an operational environment that mainlyrelies on a TDM (Time Division Multiplexing) service and evolves to IPin an applied scenario.

A typical MPLS-TP tunnel protection generally uses a 1+1 protection modeand a 1:1 protection mode.

In the 1+1 protection mode, a source PE (Provider Edge) device transmitsat a head node a tunnel traffic on both a primary tunnel and a backuptunnel, and a receiving device selects at a tail node a currently activetunnel, receives a traffic from the tunnel, and discards a traffic fromthe other tunnel. The primary tunnel is used normally. When the primarytunnel is unavailable, a switching between the primary and backuptunnels is triggered. The tail node selects an active tunnel, andtraffic will be received from the backup tunnel.

In the 1:1 protection mode, the source PE device preselects at the headnode an active tunnel and forwards a tunnel traffic on a designatedtunnel, and the receiving device receives the traffic at the tail node.The primary tunnel is used normally. When the primary tunnel isunavailable, a switching between the primary and backup tunnels istriggered. The head node chooses to transmit the traffic on the backuptunnel.

The typical MPLS-TP tunnel protection strategy directly uses a commonprotection strategy of the primary and backup tunnels, so it isimpossible to enable load sharing between the primary and backuptunnels.

When implementing a tunnel protection technique in an MPLS-TP network, aplurality of tunnels may be configured to protect one another, whereinthe number of primary tunnels is 1 and the number of protection tunnelsis N. Even if N backup tunnels are used to protect one primary tunnel,when a switching between the primary and backup tunnels occurs, only onetunnel can be selected from the backup tunnels to be an active tunnelaccording to a preferred strategy. For ease of use, only one backuptunnel may be used, and the common tunnel protections are a 1:1 tunnelprotection mode and a 1+1 tunnel protection mode.

If the 1:1 tunnel protection mode is used, data traffic in the MPLS-TPnetwork is normally transmitted via the primary tunnel. When a faultoccurs in the primary tunnel, a PE device will switch user traffic ontothe backup tunnel to be transmitted, and after the primary tunnelrecovers, the traffic on the backup tunnel will be switched back to theprimary tunnel. That is, the backup tunnel normally does not participatein traffic forwarding. However, in fact, the backup tunnel is also alogic channel pre-created on a signaling protocol, which may participatein data message forwarding. User's data traffic can be evenly shared atsource and destination nodes, and a destination device can signal thesource PE device to adjust the traffic on the primary and backup tunnelsin real time.

Based on the above concept, examples of the present disclosure provide asolution for enabling load balancing for MPLS-TP so as to realize loadsharing among the primary and backup tunnels. The examples of thepresent disclosure develop the MPLS-TP tunnel technique and enrich the1+1, 1:1 and 1:N protection schemes for the MPLS-TP tunnels, making theprotection of the MPLS-TP tunnels more efficient and perfect.

The examples of the present disclosure are described in detail belowwith reference to the drawings.

Referring to FIG. 1, a schematic diagram of a flow of balancing loadaccording to an example of the present disclosure is shown. An MPLS-TParchitecture adopted in the flow includes PE1 and PE2 with N (N≧2)tunnels between PE1 and PE2, and these tunnels adopt a protectionmechanism of primary and backup tunnels. For data transmission betweenthe PEs, transmission periods are specified in a system, and in eachtransmission period, a source PE device performs load balancing amongthe tunnels based on transmission performance of each tunnel fed back bya destination PE device. A length of a transmission period may be setaccording to a practical need or a network environment. For example, incase of a stable network environment, a longer transmission period maybe set so as to reduce a burden of performing calculation and processingfor balancing load on the PE devices; and in case of a less stablenetwork environment, a shorter transmission period may be set so as totimely perform the calculation and processing for balancing load basedon tunnel variations. Moreover, the example of the present disclosurerequires the destination PE device (i.e. a PE device located at a tailnode of a tunnel) to periodically feed back transmission performanceinformation about each tunnel to the source PE device (i.e. a PE devicelocated at a head node of the tunnel), so that the source PE device mayperform load balancing among the tunnels based on the information.

The flow shown in FIG. 1 depicts a process of enabling load balancing bytaking data transmission from PE1 to PE2 as an example. As illustrated,when a transmission period comes, the flow may include blocks 101 and102. In block 101, PE1 allocates traffic to each of the N tunnels in acurrent transmission period based on transmission performanceinformation about each of the N tunnels in a previous transmissionperiod fed back by PE2. In block 102, PE1 obtains the traffic allocatedto each of the N tunnels and transmits data to PE2 via the correspondingtunnels.

PE2 may feed back to PE1 the transmission performance information abouteach of the N tunnels when the transmission period comes, or it may feedback to PE1 the transmission performance information about each of the Ntunnels based on a set feedback period. In the latter case, the feedbackperiod should be set in such a way as to enable PE1 to receive thetransmission performance information about each of the N tunnels in theprevious transmission period fed back by PE2 upon or prior to reachingthe transmission period.

In each transmission period, PE1 performs load sharing for datatransmitted to PE2 on the N tunnels in the above-mentioned manner, thusduring the whole transmission process, load sharing for the traffic fromPE1 to PE2 on the N tunnels is realized.

In the above flow, the source PE device allocates traffic based on thetransmission performance information about each tunnel sent from thepeer PE in each transmission period, regardless of whether there is anydata message to be transmitted at this time. If there are data messagesto be transmitted, traffic allocation of each tunnel is obtained duringthe transmission (e.g. parameters of the load sharing) and the datamessages are transmitted in sequence according to these parameters. Itcan be seen that in the example of the present disclosure, no softwareintervention is needed during data forwarding, while as for thesoftware, it is only required to maintain tunnel information in a loadbalancing module. Transmitting data messages and allocating tunneltraffic are asynchronous, and a relationship therebetween is thatparameters of the load sharing need to be obtained before transmittingthe data messages, and then the data messages are transmitted.

Various examples of the destination PE device (i.e. PE2) feeding backthe transmission performance information about the tunnels and thesource PE device (i.e. PE1) performing the traffic load sharing in theabove-mentioned flow are described in detail below.

In order to feed back the transmission performance information abouteach tunnel from the destination PE device to the source PE device, inthe example of the present disclosure, an inverse MPLS tunnel isestablished between the source PE device and the destination PE device,and the destination PE device may feed back the transmission performanceinformation about N tunnels to the source PE device via the establishedinverse MPLS tunnel. Of course, if there is already the inverse tunnelbetween the source PE device and the destination PE device, thetransmission performance information about N tunnels may be fed back tothe source PE device via the inverse tunnel.

In an example, the transmission performance information about N tunnelsmay be transmitted together to the source PE device through an indicatormessage, or indicator messages may be transmitted in sequence to thesource PE device so as to transmit the transmission performanceinformation about each tunnel to the source PE device, wherein eachmessage is only used to transmit transmission performance informationabout one tunnel. The transmission performance information herein may bestatistical information obtained by the destination PE device based onmessage reception conditions, such as the statistical number of messagesreceived from each of the tunnels, a delay or a packet loss rate, etc.,or any combination thereof.

The indicator message may directly use an OAM protocol message aftersome proper extension to the protocol message is made. Such messages asCV (Connectivity Verification), FFD (Fast Failure Detection), BDI(Backward Defect Indicator), and FDI (Forward Defect Indicator) of MPLSOAM all use reserved 14 labels as a load identity, and behind the 14labels, there is an MPLS OAM message load of 44 octets as shown in FIG.2. Currently, seven types of MPLS OAM messages may be differentiatedaccording to their functions, and table 1 shows the seven types ofmessages as well as their values and meanings in an OAM function typecodepoint field:

TABLE 1 OAM function type First octet of OAM packet payload codepoint(Hex) function type and purpose 00 Reserved 01 CV (ConnectivityVerification) 02 FDI (Forward Defect Indicator) 03 BDI (Backward DefectIndicator) 04 Reserved for Performance packets 05 Reserved for LB-Req(Loopback Request) 06 Reserved for LB-Rsp (Loopback Response)

On the basis of these existing OAM function types, the example of thepresent disclosure makes some proper extension. For example, a new typeof OAM function type codepoint is added as 07 to be used for BNI(Backward Notify Indicator), and a data packet structure thereof may beas shown in FIG. 2. The Notify Value carries information about theindicated tunnel, such as information including a current traffic, adelay, a packet loss rate, etc.

The transmission performance information about each tunnel fed back bythe destination PE device will be used as the basis for the source PEdevice to balance traffic load among the tunnels. The source PE deviceof the MPLS-TP tunnel, after receiving the information, readjusts aforwarding strategy of N tunnels to reallocate the traffic to each ofthe tunnels, thereby flexibly controlling the traffic carried on thetunnels. If traffic of a certain tunnel that carries data traffic is toolarge, the traffic allocated to the tunnel in a next time slot will bereduced. Likewise, if the traffic of a certain tunnel is too small, thetraffic allocated to the tunnel in the next time slot will be increased.

As for block 102 in the flow shown in FIG. 1, the example of the presentdisclosure enables load sharing in the MPLS tunnels by means of timedivision multiplexing based on QoS instead of using header content of anoriginal message as a KEY of Hash algorithm. Specifically, the source PEdevice allocates to each of the tunnels a time slot occupied fortransmitting data in a current transmission period based on thetransmission performance information about each of the primary andbackup tunnels in a previous transmission period, wherein a time slotallocated to a tunnel with a high transmission performance is longerthan a time slot allocated to a tunnel with a low transmissionperformance, and time slots allocated to the tunnels do not overlap oneanother to make sure that data is transmitted via only one tunnel in thecurrent moment. After allocating the time slots for data transmission tothe tunnels, the source PE device, in the time slots allocated to thecorresponding tunnels, transmits data to the destination PE device viathe tunnels. For example, the source PE device selects an outgoinginterface of the corresponding tunnel when the corresponding time slotcomes based on time slot allocation of each tunnel, and forwards datamessages via the outgoing interface.

In an example, the source PE device determines a transmissionperformance proportion of each of the tunnels based on the transmissionperformance information about each of the tunnels, and divides thecurrent transmission period into a number of time slots. Then, thesource PE device allocates the time slots of the current transmissionperiod to the tunnels based on the transmission performance proportionsof the tunnels. The source PE device transmits data to a tunnel to betransmitted only in the time slot allocated to the tunnel, so that eachof the tunnels can transmit data only in the time slot allocatedthereto, but it cannot transmit data in the time slot that is notallocated to it. In this case, only one tunnel carries data traffic atthe current moment. When dividing the current transmission period intotime slots, a tunnel with the worst transmission performance isguaranteed to have at least one time slot allocated thereto. When allthe tunnels have the same transmission performance (e.g. a QoSattribute), each of the tunnels has the same number of time slotsallocated thereto.

For example, there are three tunnels between PE1 and PE2, and PE1calculates that transmission performance proportions of tunnel 1, tunnel2 and tunnel 3 are 1:2:3 based on a transmission performance parameterof each tunnel fed back by PE2 (wherein tunnel 3 has the besttransmission performance). In this case, PE1 may divide a currenttransmission period into 6 time slots, and allocate one time slot (e.g.time slot 1) to tunnel 1, two time slots (e.g. time slot 2 and time slot3) to tunnel 2, and three time slots (e.g. time slots 4-6) to tunnel 3.Hence, PE1 transmits data via tunnel 1 in time slot 1, transmits datavia tunnel 2 in time slots 2 and 3, and transmits data via tunnel 3 intime slots 4-6. It can be seen that after calculating the transmissionperformance proportions of the tunnels, by using a sum of values of theproportions (or an integral multiple of the sum) as the number of timeslots of the current transmission period (for example, 1+2+3=6 in caseof the above-mentioned 1:2:3), it is guaranteed that each tunnel has atleast one time slot allocated thereto.

It can be seen that by dividing time slots for N tunnels according to acertain proportion, there is traffic on only one tunnel in each timeslot, while there is no traffic on other tunnels, so that an even loadon the tunnels can be realized in one transmission period.

If a bandwidth reservation is realized on public network tunnels of theMPLS-TP, equal and balanced load on the tunnels can be realized in thisway. For example, there are N MPLS-TP tunnels, and their bandwidths arerespectively d1, d2, . . . , dn. A bandwidth of user's VPN (VirtualPrivate Network) service carried on the N tunnels may be greater than asingle MPLS-TP tunnel. So all the existing MPLS-TP tunnels cannot meetthe requirement, and when the user's VPN service is carried on anMPLS-TP tunnel, a priority packet loss occurs. If these N MPLS-TPtunnels are aggregated, equal load balancing can be realized among theMPLS-TP tunnels, and the user's VPN traffic is evenly shared among theMPLS-TP tunnels.

In the example of the present disclosure, further, the MPLS-TP tunnelsmay also form a tunnel equalization group. The N tunnels are membertunnels of the tunnel equalization group, and each of the MPLS-TPtunnels is detected through MPLS OAM to monitor connectivity of thetunnels in real time, as shown in FIG. 3.

After setting the tunnel equalization group, state changes of the membertunnels may influence a state of the whole tunnel equalization group.State changes of the tunnel equalization group include the followingcases:

a first case: there is at first no member tunnel in the tunnelequalization group, after a first member tunnel is added, the state ofthe tunnel equalization group changes from DOWN to UP, and the bandwidththereof is the bandwidth of the first member tunnel;

a second case: there are member tunnels in the tunnel equalization groupat first, when one more member tunnel is added, the state of the tunnelequalization group does not change, which is still UP, and the bandwidththereof is a sum of the bandwidths of the member tunnels;

a third case: there are member tunnels in the tunnel equalization group,when one member tunnel exits, there are still other member tunnels, andthe state of the tunnel equalization group does not change, which isstill UP, and the bandwidth thereof is a sum of the bandwidths of theremaining member tunnels; and

a fourth case: when the last member tunnel of the tunnel equalizationgroup exits, the state of the tunnel equalization group changes from UPto DOWN, indicating that the tunnel equalization group is unavailable.

The bandwidth of the tunnel equalization group is equal to a sum of thebandwidths of all the member tunnels, and the tunnel equalization groupneeds to respond to a detection state indicator of a single tunnel inreal time. When a state of a tunnel changes from DOWN to NORMAL, abandwidth of the tunnel is added to the bandwidth of the tunnelequalization group. That is, the tunnel is added to the tunnelequalization group as a member thereof. At this time, user traffic isshared evenly among the member tunnels of the tunnel equalization group.When a state of a tunnel changes from NORMAL to DOWN, a bandwidth of thetunnel is subtracted from the bandwidth of the tunnel equalizationgroup. That is, the tunnel exits from the tunnel equalization group. Atthis time, user traffic is shared among the remaining member tunnels ofthe tunnel equalization group.

Based on the same technical concept, the examples of the presentdisclosure also provide a PE device, which may be applied to theabove-mentioned flow.

Referring to FIG. 4, a schematic block diagram of a PE device accordingto an example of the present disclosure is shown. There are at least twotunnels between the PE device and a peer PE device, and a protectionmechanism of primary and backup tunnels is used. The PE device is adestination PE device located at a tail node of a tunnel, and asillustrated, the PE device may comprise:

an information feedback module 401 to periodically feed backtransmission performance information about each of the primary andbackup tunnels to a source PE device located at a head node of thetunnel (e.g. feed back the transmission performance information abouteach of the primary and backup tunnels in a previous transmissionperiod); the transmission performance information about the tunnels fedback by the information feedback module may include one of or anycombination of the following information: the number of receivedmessages, a data transmission delay, and a packet loss rate; and

a receiving module 402 to receive data transmitted by the source PEdevice located at the head node of the tunnel,

wherein said source PE device is to allocate traffic to each of theprimary and backup tunnels in a current transmission period based on thetransmission performance information about each of the primary andbackup tunnels in the previous transmission period fed back by thedestination PE device located at the tail node of the tunnel when a settransmission period comes, obtain the traffic allocated to the tunnels,and transmit data to the destination PE device via the correspondingtunnels.

Further, the information feedback module 401 may comprise an extendedOAM protocol message, which feeds back the transmission performanceinformation about each of the primary and backup tunnels to the sourcePE device.

Referring to FIG. 5, a schematic block diagram of a PE device accordingto a further example of the present disclosure is shown. There are atleast two tunnels between the PE device and a peer PE device, and aprotection mechanism of primary and backup tunnels is used. The PEdevice is a source PE device located at a head node of a tunnel, and asillustrated, the PE device may comprise:

a receiving module 501 to receive transmission performance informationabout each of the primary and backup tunnels fed back periodically by adestination PE device located at a tail node of the tunnel;

a load balancing module 502 to allocate traffic to each of the primaryand backup tunnels in a current transmission period based on thetransmission performance information about each of the primary andbackup tunnels in a previous transmission period fed back by thedestination PE device located at the tail node of the tunnel when a settransmitting period comes; and

a transmitting module 503 to obtain the traffic allocated to each of thetunnels, and transmit data to the destination PE device via thecorresponding tunnels.

Further, the load balancing module 502 may allocate to each of thetunnels a time slot occupied for transmitting data in the currenttransmission period based on the transmission performance informationabout each of the primary and backup tunnels in the previoustransmission period, wherein a time slot allocated to a tunnel with ahigh transmission performance is longer than a time slot allocated to atunnel with a low transmission performance, and time slots allocated tothe tunnels do not overlap one another. Accordingly, the transmittingmodule 503 may transmit the obtained data to the destination PE devicevia the tunnels in the time slots allocated to the tunnels by the loadbalancing module 502. In an example, the load balancing module 502 maydetermine a transmission performance proportion of each of the primaryand backup tunnels based on the transmission performance information,divide the current transmission period into a number of time slots, andthen allocate the time slots of the current transmission period to theprimary and backup tunnels based on the transmission performanceproportion of each of the primary and backup tunnels, wherein whendividing the current transmission period into time slots, a tunnel withthe worst transmission performance is guaranteed to have at least onetime slot allocated thereto.

In the above-mentioned PE device, the primary and backup tunnels aremember tunnels of a tunnel equalization group. Accordingly, the PEdevice may also comprise a tunnel equalization group maintaining module504 that removes a member tunnel from the tunnel equalization group whena state of the member tunnel of the tunnel equalization group changesfrom NORMAL to DOWN, and adds a tunnel to the tunnel equalization groupwhen a state of the tunnel changes from DOWN to NORMAL. Accordingly, theload balancing module 502 allocates traffic to each of the membertunnels in the tunnel equalization group in the current transmissionperiod.

In an example, the load balancing module 502 in the above-mentioneddevice receives in each transmission period an OAM message transmittedfrom the peer PE, and allocates traffic to the MPLS-TP tunnels in thetunnel equalization group through information carried in the OAM messageregardless of whether the transmitting module 503 has any data messageto be transmitted at this time. If the transmitting module 503 has datamessages to be transmitted, it obtains a time slot parameter of each ofthe tunnels from the load balancing module 502 during the transmission,and transmits the messages in sequence according to these parameters.Such processing as transmission, reception and analysis of the OAMmessage as well as maintenance of the tunnel equalization group(bandwidth, allocation of time slots, and tunnel state UP/DOWN) isrealized by software. In terms of hardware, data messages aretransmitted according to time slots and bandwidths.

In the examples of the present disclosure, by setting transmissionperiods and requesting the destination PE device to feed back thetransmission performance information about each of the primary andbackup channels to the source PE device, when a transmission periodcomes, the source PE device may allocate traffic to each of the primaryand backup tunnels in a current transmission period based on thetransmission performance information about each of the primary andbackup tunnels in a previous transmission period fed back by thedestination PE device, and may transmit the obtained data to thedestination PE device via the corresponding tunnels based on situationsof allocation, thus enabling load balancing among the primary and backuptunnels in real time based on transmission performance of each of theprimary and backup tunnels.

In summary, the examples of the present disclosure expand the MPLS-TPtunnel technique, realize complete sharing of load, and provide a moreefficient protection measure and tunnel load balancing technique.

The above examples can be implemented by hardware, software or firmwareor a combination thereof. For example, the various methods, processesand functional modules described herein may be implemented by aprocessor (the term processor is to be interpreted broadly to include aCPU, processing unit, ASIC, logic unit, or programmable gate arrayetc.). The processes, methods and functional modules may all beperformed by a single processor or split between several processers;reference in this disclosure or the claims to a “processor” should thusbe interpreted to mean “one or more processors”. The processes, methodsand functional modules may be implemented as machine readableinstructions executable by one or more processors, hardware logiccircuitry of the one or more processors or a combination thereof.Further the teachings herein may be implemented in the form of asoftware product. The computer software product is stored in a storagemedium and comprises a plurality of instructions for making a computerdevice (which can be a personal computer, a server or a network devicesuch as a router, switch, access point etc.) implement the methodrecited in the examples of the present disclosure.

All of the features disclosed in this specification (including anyaccompanying claims, abstract and drawings), and/or all of the processesor blocks of any method so disclosed, may be combined in anycombination, except combinations where at least some of such featuresand/or processes or blocks are mutually exclusive.

Each feature disclosed in this specification (including any accompanyingclaims, abstract and drawings), may be replaced by alternative featuresserving the same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

The figures are only illustrations of an example, wherein the modules orprocedure shown in the figures are not necessarily essential forimplementing the present disclosure. Moreover, the sequence numbers ofthe above examples are only for description, and do not indicate anexample is more superior to another.

Those skilled in the art can understand that the modules in the devicein the example can be arranged in the device in the example as describedin the example, or can be alternatively located in one or more devicesdifferent from that in the example. The modules in the aforesaid examplecan be combined into one module or further divided into a plurality ofsub-modules.

Although the flow diagrams described above show a specific order ofexecution, the to order of execution may differ from that which isdepicted. For example, the order of execution of two or more blocks maybe scrambled relative to the order shown. Also, two or more blocks shownin succession may be executed concurrently or with partial concurrence.All such variations are within the scope of the present disclosure.

What is claimed is:
 1. A method of enabling load balancing forMultiprotocol Label Switching Transport Profile (MPLS-TP), applied to aprocess of transmitting data between two Provider Edge (PE) devices thatadopt a protection mechanism of primary and backup tunnels, wherein themethod comprises: allocating, by a source PE device located at a headnode of a tunnel, traffic to each of the primary and backup tunnels in acurrent transmission period based on transmission performanceinformation about each of the primary and backup tunnels in a previoustransmission period fed back by a destination PE device located at atail node of the tunnel, when a set transmission period comes, whereinsaid allocating comprises: allocating, by said source PE device, timeslots to both the primary and backup tunnels for transmitting data inthe current transmission period based on the transmission performanceinformation about each of the primary and backup tunnels in the previoustransmission period, wherein the time slots allocated to both theprimary and backup tunnels do not overlap with one another; andobtaining, by said source PE device, the traffic allocated to each ofthe tunnels and transmitting data to the destination PE device in thetime slots via the primary and backup tunnels.
 2. The method as claimedin claim 1, wherein the transmission performance information about thetunnels comprises one of or any combination of the followinginformation: a number of received messages, a data transmission delay,and a packet loss rate.
 3. The method as claimed in claim 1, whereinsaid destination PE device feeds back the transmission performanceinformation about each of the primary and backup tunnels to said sourcePE device by means of an extended Operation, Administration andMaintenance (OAM) protocol message.
 4. The method as claimed in claim 1,wherein a time slot of the time slots allocated to a tunnel of theprimary or backup tunnels with a high transmission performance is longerthan a time slot of the time slots allocated to a tunnel of the primaryor backup tunnels with a low transmission performance.
 5. The method asclaimed in claim 4, wherein said allocating to each of the tunnels atime slot occupied for transmitting data in the current transmissionperiod based on the transmission performance information about each ofthe primary and backup tunnels in the previous transmission periodcomprises: allocating a plurality of the time slots of the currenttransmission period to each of the primary and backup tunnels based onthe transmission performance proportion of each of the primary andbackup tunnels, wherein when dividing the current period into timeslots, a tunnel with the worst transmission performance is guaranteed tohave at least one time slot allocated thereto.
 6. The method as claimedin claim 1, wherein each of the primary and backup tunnels is a membertunnel of a tunnel equalization group, and wherein the method furthercomprises: when a state of a member tunnel of said tunnel equalizationgroup changes from NORMAL to DOWN, removing the member tunnel from thetunnel equalization group, and when a state of a tunnel changes fromDOWN to NORMAL, adding the tunnel to the tunnel equalization group; andwherein said allocating traffic to each of the primary and backuptunnels in the current transmission period comprises allocating trafficto each of the member tunnels in said tunnel equalization group in thecurrent transmission period.
 7. A destination Provider Edge (PE) devicefor setting up at least two tunnels between said destination PE deviceand a peer PE device and a protection mechanism of primary and backuptunnels, said destination PE device located at a tail node of a tunnel,wherein said destination PE device comprises: an information feedbackmodule to periodically feed back transmission performance informationabout each of the primary and backup tunnels to a source PE devicelocated at a head node of the tunnel; and a receiving module to receivedata transmitted by the source PE device located at the head node of thetunnel, wherein said source PE device is to allocate traffic to each ofthe primary and backup tunnels in a current transmission period based onthe transmission performance information about each of the primary andbackup tunnels in a previous transmission period fed back by thedestination PE device located at the tail node of the tunnel when a settransmission period comes, wherein to allocate the traffic, the sourcePE device is to allocate time slots to both the primary and backuptunnels for transmitting data in the current transmission period basedon the transmission performance information about each of the primaryand backup tunnels in the previous transmission period, wherein the timeslots allocated to both the primary and backup tunnels do not overlapwith one another, and the source PE device is to obtain the trafficallocated to each of the tunnels, and transmit data to the destinationPE device in the time slots via the primary and backup tunnels.
 8. Thedestination PE device as claimed in claim 7, wherein the transmissionperformance information about the tunnels fed back by said informationfeedback module comprises one of or any combination of the followinginformation: a number of received messages, a data transmission delay,and a packet loss rate.
 9. The destination PE device as claimed in claim7, wherein said information feedback module is to feed back thetransmission performance information about each of the primary andbackup tunnels to said source PE device by means of an extendedOperation, Administration and Maintenance (OAM) protocol message. 10.The destination PE device as claimed in claim 7, wherein the source PEdevice is to allocate a plurality of the time slots of the currenttransmission period to each of the primary and backup tunnels based onthe transmission performance proportion of each of the primary andbackup tunnels, wherein when dividing the current period into timeslots, a tunnel with the worst transmission performance is guaranteed tohave at least one time slot allocated thereto.
 11. A Provider Edge (PE)device for setting up at least two tunnels between said PE device and apeer PE device and a protection mechanism of primary and backup tunnels,said PE device being a source PE device located at a head node of atunnel, wherein said PE device comprises: a receiving module to receivetransmission performance information about each of the primary andbackup tunnels fed back periodically by a destination PE device locatedat a tail node of the tunnel; a load balancing module to allocatetraffic to each of the primary and backup tunnels in a currenttransmission period based on the transmission performance informationabout each of the primary and backup tunnels in a previous transmissionperiod fed back by the destination PE device located at the tail node ofthe tunnel when a set transmission period comes, wherein to allocate thetraffic, the load balancing module is to allocate time slots to both theprimary and backup tunnels for transmitting data in the currenttransmission period based on the transmission performance informationabout each of the primary and backup tunnels in the previoustransmission period, wherein the time slots allocated to both theprimary and backup tunnels do not overlap with one another; and atransmitting module to obtain the traffic allocated to each of thetunnels, and transmit data in the time slots to the destination PEdevice via the primary and backup tunnels.
 12. The PE device as claimedin claim 11, wherein a time slot of the time allocated to a tunnel ofthe primary and backup tunnels with a high transmission performance islonger than a time slot allocated to a tunnel of the primary and backuptunnels with a low transmission performance.
 13. The PE device asclaimed in claim 12, wherein said load balancing module is to allocate aplurality of the time slots of the current transmission period to eachof the primary and backup tunnels based on the transmission performanceproportion of each of the primary and backup tunnels, wherein whendividing the current period into time slots, a tunnel with the worsttransmission performance is guaranteed to have at least one time slotallocated thereto.
 14. The PE device as claimed in claim 11, whereineach of the primary and backup tunnels is a member tunnel of a tunnelequalization group; wherein said PE device further comprises a tunnelequalization group maintaining module to remove a member tunnel from thetunnel equalization group when a state of the member tunnel of saidtunnel equalization group changes from NORMAL to DOWN, and add a tunnelto the tunnel equalization group when a state of the tunnel changes fromDOWN to NORMAL; and wherein said load balancing module is to allocatetraffic to each of the member tunnels in said tunnel equalization groupin the current transmission period.